Unlocking the Second Electron in the Electrochemical Delithiation/Lithiation of Copper (2,5-Dilithium-oxy)-Terephthalate via a Carbon-Supported Electrode Architecture

Copper (2,5-dilithium-oxy)-terephthalate (Cu(Li₂)-p-DHT) is synthesized and thoroughly characterized using a range of analytical techniques, then evaluated electrochemically as a lithiated host material for positive electrodes in Li half-cells. When formulated as a carbon-supported organic electrode material, the compound reaches its full theoretical two-electron capacity, delivering a specific capacity of 188.2 mAh g^-1, almost double that of previously reported M(Li₂)-p-DHT analogs (≈100 mAh g^-1). However, its cycling stability remains limited due to the formation of a fully oxidized quinone species in the delithiated state, as evidenced by fourier-transform infrared spectroscopy. This oxidized form is found partially soluble in carbonate-based electrolytes, resulting in poor cycling performance. By narrowing the potential window to the one-electron storage reaction, cycling performance improves significantly, with 96% capacity retention after 50 cycles and a coulombic efficiency exceeding 99%, albeit at a reduced capacity of ≈80 mAh g^-1. Electron energy-loss spectroscopy further confirmed the gradual structural evolution from the semiquinone to quinone form. These results highlight key design principles for enhancing lithium extraction in lithiated organic host materials and represent a significant step toward achieving capacities that approach those of conventional inorganic electrodes.